1. Field of the Invention
The present invention relates to a toner for use in an image forming method such as electrophotography, electrostatic printing, a magnetic recording method, or a toner jet method.
2. Description of the Related Art
Various toners have been heretofore proposed in order that fixability at a low temperature and hot offset resistance at a high temperature be compatible with each other. In particular, a toner using a binder resin having a polyester component has been used in a model such as a high-speed device where importance is placed on fixing performance because of its superior fixability and hot offset property. However, a polyester resin tends to contain water because the polyester resin is polymerized by a dehydration reaction. Moreover, the polyester resin tends to adsorb water owing to the presence of an acid group or a hydroxyl group at a terminal of its molecule. Therefore, the polyester resin is susceptible to the temperature and humidity of its use environment, so environmental characteristics of developability and chargeability of the toner tend to be unstable.
Machines such as a printer are required to achieve miniaturization from the viewpoints of energy conservation and space saving in an office, and containers for storing toners are also required to achieve miniaturization. Therefore, a toner enabling low toner consumption, that is, a toner with which many sheets can be printed out using only a small amount of the toner, has been demanded.
In the case where a binder resin having a polyester component is used for a magnetic toner, it is extremely important to control magnetic properties of the toner and the charging property of the binder resin to achieve low toner consumption. In particular, a polymerization catalyst for producing a polyester resin is important to enhance environmental stability of developability of the toner and to achieve low toner consumption because the polymerization catalyst has a profound effect on the charging property of the binder resin.
According to the techniques generally performed for producing a polyester resin for a toner, a tin-based catalyst such as dibutyltin oxide and dioctyltin oxide, or an antimony-based catalyst such as antimony trioxide is used as the polymerization catalyst. Those techniques are inadequate to provide the performance required of a magnetic toner, that is, a higher speed and greater environmental stability which will be further demanded from now on.
JP 2002-148867 A discloses a technique of using a titanate of an aromatic diol as a polymerization catalyst. JP 2001-064378 A discloses a technique of using a solid titanium compound as a polymerization catalyst.
However, polymerization of a polyester component through the use of a polymerization catalyst made of each of those titanium compounds is not adequate for controlling the chargeability of a magnetic toner.
In a one-component developing method using a magnetic toner which is preferably used in an electrophotographic developing method, the magnetic properties and chargeability of the magnetic toner significantly affect the toner consumption. In particular, in a magnetic toner using a polyester resin as its binder resin, it is necessary to comprehensively control chargeability, dispersibility of a magnetic iron oxide, magnetic properties of the magnetic toner, and so on by a combination of the resin and a magnetic material. JP 09-090670 A, JP 09-146297 A, JP 10-171150 A, and JP 2002-214829 A each disclose magnetic properties of a toner. However, a polymerization catalyst for a polyester component and magnetic properties of a toner are not sufficiently studied in those publications, and thus there remains room for improvement.
JP 03-084558 A, JP 03-229268 A, and JP 04-001766 A each disclose a technique of forming a toner into an approximately spherical shape by means of a production method such as a spray granulation method, a dissolution method, or a polymerization method as a technique of modifying the shape of a toner. In addition, JP 02-087157 A, JP 10-097095 A, JP 11-149176 A, and JP 11-202557 A each disclose a technique of modifying the shape and surface characteristics of a particle of a toner produced by a pulverization method by applying a thermal or mechanical impact. However, modifying the shape of a toner by each of those methods alone does not facilitate a reduction in toner consumption while maintaining high environmental stability of developability of a magnetic toner using a polyester resin.